EXHIBIT 5.1
                            GRAUBARD MOLLEN & MILLER
                                600 Third Avenue
                          New York, New York 10016-2097


   
                                                              January  28, 1997
    


H.E.R.C. Products Incorporated
2202 West Lone Cactus Drive, Suite 15
Phoenix, Arizona  85027

Dear Sirs:

   
         Reference   is  made  to  the   Registration   Statement  on  Form  S-3
("Registration  Statement") filed by H.E.R.C.  Products Incorporated ("Company")
under the  Securities  Act of 1933,  as  amended  ("Act"),  with  respect  to an
aggregate of 1,938,631 shares of common stock, par value $.01 per share ("Common
Stock")  to be  offered  and sold by those  persons  listed in the  Registration
Statement  as  Selling  Stockholders  ("Selling  Stockholders"),  including  (i)
1,603,631  shares of Common Stock to be issued by the Company upon conversion of
170,000  shares of Series A Preferred  Stock  ("Preferred  Stock") , (ii) 85,000
shares of  Common  Stock to be issued by the  Company  upon  exercise  of 85,000
Warrants issued to Perrin,  Holden & Davenport Capital Corp. ("PHD Warrants" and
"PHD,"  respectively),  (iii) 200,000 shares of Common Stock to be issued by the
Company upon exercise of 200,000  Warrants issued to GKN Securities  Corp. ("GKN
Warrants" and "GKN,"  respectively) and (iv) 50,000 shares of Common Stock to be
issued by the  Company  upon  exercise of 50,000  Warrants  issued to The Equity
Group, Inc.
    
("EGI Warrant" and "EGI," respectively).

         We have examined such documents and considered such legal matters as we
have deemed necessary and relevant as the basis for the opinion set forth below.
With  respect  to such  examination,  we have  assumed  the  genuineness  of all
signatures,  the authenticity of all documents submitted to us as originals, the
conformity to original documents of all documents  submitted to us as reproduced
or  certified  copies,  and the  authenticity  of the  originals of those latter
documents.  As to questions of fact  material to this  opinion,  we have, to the
extent  deemed  appropriate,  relied  upon  certain  representations  of certain
officers and employees of the Company.

   
         Based  upon the  foregoing,  it is our  opinion  that (i) the shares of
Common Stock being registered on the Registration Statement, to be issued by the
Company to certain of the Selling  Stockholders upon conversion of the Preferred
Stock  have been  duly  authorized  and,  when  issued  upon  conversion  of the
Preferred  Stock in accordance  with the terms thereof,  will be legally issued,
fully  paid and  non-assessable,  and (ii) the  shares  of  Common  Stock  being
registered on the Registration Statement, to be issued by the Company to certain
Selling  Stockholders  upon  exercise of the PHD  Warrants,  GKN Warrant and EGI
Warrant  have been duly  authorized  and,  when sold and paid for in the  manner
provided in the Registration  Statement and the warrant  agreements between PHD,
GKN and EGI and the Company,  respectively,  will be legally issued,  fully paid
and non-assessable.
    

         In giving this opinion,  we have assumed that, prior to their issuance,
all  certificates for the Company's shares of Common Stock will be duly executed
on behalf of the Company by the Company's  transfer  agent and registered by the
Company's registrar, if necessary, and will conform, except as to denominations,
to specimens which we have examined.

         We hereby  consent  to the use of this  opinion  as an  exhibit  to the
Registration  Statement,  to the use of our  name as  your  counsel,  and to all
references  made  to us in the  Registration  Statement  and  in the  Prospectus
forming a part thereof.  In giving this consent,  we do not hereby admit that we
are in the category of persons whose consent is required  under Section 7 of the
Act, or the rules and regulations promulgated thereunder.

                                                  Very truly yours,

                                                  /s/ Graubard Mollen & Miller

                                                 GRAUBARD MOLLEN & MILLER